Fuse structures with ferrules of insulating material



Feb. 17, 1959 P. c. JACOBS, JR., ETAL FUSE STRUCTURES WITH FERRULES OF INSULATING MATERIAL Filed. Sept. 3, 1957 United States Patent O FUSE STRUCTURES WITH FERRULES F INSULATING MATERXAL Philip C. llacobs, Jr., Newtonville, Mass., and Kenneth W. Swain, Hampton'Falls, N. H., assignors to The `Chase-Shawmut Company, Newburyport, Mass.`

Application September 3, 1957, Serial No. 681,537

Claims. (Cl. 200-131) This invention relates to electric fuses, and more particularly to electric fuses having a pair of blade contacts for connecting the fuses into an electric circuit.

It is possible to achieve a substantial reduction of size by providing electric fuses with caps of an insulating material, preferably a suitable elastomer, or synthetic rubber. This has been shown in detail in the copending patent application of Kenneth W. Swain, Current-Limiting Fuses of Reduced Size, tiled April 26, 1957, Ser. No. 655,288.

It is one object of this invention to improve the structure disclosed in the aforementioned, patent application.

The fusible elements or fuse links of current-limiting fuses having relatively small letfthrough current peaks must be provided with one or more points of drastically reduced cross-sectional area. As a result, this particular type of current-limiting fuses is relatively fragile, i. e. there is a danger of breakage lof the fusible elements or fuse links on sudden impact as may occur in transit, or on careless handling of fuse structures.

lt is, therefore, another-object of the invention to provide electric fuses with caps which have shock-absorbing properties in addition to the normal sealing function of fuse caps.

Since copper tends to oxidize rapidly, thereby forming on copper surfaces oxide films which result in a high contact resistance it is desirable, if not imperative, to silver-plate the blade contacts of electric fuses. The presence of. certain chemicals, e. g. of sulphur, adjacent silver plated contacts is incompatible with the silver plating thereon.

It. is, therefore, another object of the invention to provide fuses having silver plated blade contacts and having insulating caps made of a plastic material cornpatibl'e with the presence of silver, said caps being bonded to the fuse vstructure by adhesive means compatible with the presence of silver as well as that of the material of which the caps are made;

Still' another object 'of the invention is to provide fuses having caps extending over a portion of the casing and over a portion of the blade contacts which caps may be inseparably bonded to the casing and are inseparably bonded to the blade contacts, i. e. so firmly bonded to them that the strength of the bonds exceeds that of the caps. Under such condition the caps may rather be destroyed by application oi excessive force than removed from the fuse structure.

Still another object of the invention is to provide-elec tric fuses having simple and elective bonding means securing insulating/caps. to the fuses.

A further object of the invention is to provide electric fuses having insulatihgcaps thereon adapted to preclude insertion of `the fuses into fuse holders into which they are not. supposed to be inserted.

Further `objects and advantages of the invention will become. apparent aslthe following 4description proceeds, and the features ofr novelty which characterize the invention will be pointed out with particularity in the claims annexed to, and forming part of, this specification.

For a better understanding of the invention reference may be had to the accompanying drawing wherein Fig. 1 is .a front view of a fuse structure embodying the invention;

Fig. 2 is a vertical section of a portion of the structure of Fig. l showing that portion on a considerably larger scale than Fig. l; Y

Fig. 3 is a section taken along 3-3 of Fig. 2;

Fig. 4 is a portion of a sectiontaken along 4-4 of Fig. 2; and

Fig. 5 is a section showing -on a much larger scale than all the preceding figures the kind or" tape. used for A assembling fuses embodying theinvention.

Referring now to the drawing, numeral 1 has been applied to indicate a tubular casing of insulating ma'- terial, preferably a synthetic-resin-.glass cloth laminate. The ends of casing 1 are closed by terminal elements, preferably in the shape of copper plugs 2 pressed into casing 1 under considerable pressure, as by means of a hydraulic press. A pair of silver plated blade contac 3 projects axially outwardly from each. pair of metal plugs 2. Plugs 2 and blade contacts 3 may be formed by a forging. Figs. l and 2 show an alternative, comprising a transverse groove 2a on the outer side of each of the plugs 2 into which 'the blade contact 3 is tted and brazed. The juxtaposed internal surfaces ot plugs 2 are provided with grooves 2b receiving the ends of ribbon fuse links 4. Fuselinks 4 are perforated at 4a,

and the ends thereof received by grooves 2b are soldered to plugs 2 by solder points not shown. The two plugs 2 may be spaced by a central spacer rod Svof insulating material. The fuse links 4 conductively interconnecting plugs 2 maybe submersed in a pulverulent arc quenching ller 6 such as a chemically reasonably pure quartz sand. Reference numeral 7 has been applied to generally indicate a pair of caps` of insulating material. Since it is very desirable that the blade contacts 3 be silver-plated, and since thecaps 7 are in intimate contact with the silver-plating onA blade contacts 3, the insulating material of which caps7 areA made should be substantially free from sulphur. On the other hand, theV insulating material of which caps 7 are4 made ought to be as rubber-like as possible to provide a cushioning effeet achieving effective protection against breaking oh sleeve portion 7b deiining a duct 7c li'aving substantially the same cross-sectional configuration as each of the two blade contacts 3 and sleeve portions 7b of caps 7 are mounted on blade contacts 3. Sleeve portions 7b.may be used as a means for precluding insertion of the fuse into a fuse holder into which the vfuse ought not to be inserted. This is achieved by exposing only a certain portion of blade contacts 3 for insertion into a fuse holder.

An important aspect of the structurefshown is that .of bonding caps 7 with their axially outer sleeves or skirts 7b to the bladeV contacts 3. This must be achieved at relatively low temperatures to prevent thermal impairment of insulating casing 1. It must bel achieved by an adhesive compatible with the material ofwhich the caps 7 are made and with the silver-plating on blade contacts 3. lt ought to be achieved without resorting to an ad- Patented Fels. 1.7, 1Si59 hesive in liquid or paste'form because the internal surfaces of sleeves or skirtsV 7b are rather inaccessible and do not lend themselves to thorough surfacing with an adhesive liquid or paste. An adhesive inliquid or paste form when introduced into sleeves or skirts 7b is being scraped oft", at leastl partially, by the blade contacts when the latter are being introduced into the sleeves or skirts 7b. This results in a poor, or unacceptable, bond between these two parts 7b and 3. The situation is different in regard to the wide diameter skirt 7a which can readily be bonded to casing 1 by any appropriate adhesive in liquid or paste form. In some instances it is not even necessary to provide for a bond between skirt 7a .and casing 1, i. e. it may be sucient to rely on the resiliency of skirt 7a maintaining the latter firmly pressed against the outer lsurface of the casing 1. In most instances it is, however, desirable to establish a bond between the outer surface of casing 1 and the inner surface of skirt 7a, and the presence of such a bond is important, or imperative, where it is necessary to eiectively electrically insulate the radiallyouter ends of pins 8. Reference numeral 9 has been applied to indicate bonds between parts 7a and 1`.

The skirts 7b are bonded to blade contacts 3 either by two separate adhesive strips 16 aixed to both sides of each blade contact 3 or one single adhesive strip l0 wound around each blade contact 3. As shown inV Fig. 5, adhesive strips suitable for the purpose comprise an inner layer a of a plastic material having an epoxy resin coating 10b on each side thereof. One of coatings 10b is beingbonded to the inner surfaces of skirts 7a and the other of coatings 10b is being bonded to the surfaces of blade contacts 3. Skirts 7b cannot be removed -from blade contacts 3, however much force is being applied, and whatever tools should be used to such improper end. Application of excessive force results in tearing of caps 7, or destruction thereof, rather than their separation from blades 3.

Having disclosed a preferred embodiment of our invention it is desired that the same be not limited to the particular structure disclosed. It will be obvious to any person skilled in the art that many modications and changes may be made without departing from the broad spirit and scope of our invention. Therefore it is desired that the invention be interpreted as broadly as possible and that it be limited only as required by the prior state of the art.

We claim as our invention:

1. In an electric fuse the combination of a tubular casing of insulating material, a pair of terminal elements closing the ends of said casing, a pair of blade contacts each projecting axially outwardly from one of said pair' of terminal elements, fuse link means inside said casing conductively interconnecting said pair of terminal elements, a pair of caps of insulating material, each of said pair of caps comprising a first sleeve portion mounted on said casing and a second sleeve portion mounted on one of said pair of blade contacts, and adhesive strip means aiixed to both sides of each of said pair of blade contacts and securing said second sleeve portion of each of said pair of caps to one of said pair of blade contacts.

2. In an electric fuse the combination of a tubular casing of insulating material, a pair of terminal elements closing the ends of said casing, a pair of blade contacts each projecting axially outwardly from one of said pair of terminal elements, fuse link means inside said casing conductively interconnecting said pair of terminal elements, a pair of caps of an insulating material each comprising a first sleeve portion having an inner diameter substantially equal to the outer diameter of said casing mounted on one end of said casing, each of said pair of caps further comprising a second sleeve portion defining a duct havingA substantially the same cross-sectional configuration as each of said pair of blade contacts, said second sleeve portion of each of said pair of caps being mounted on one of said pair of blade contacts, means bonding said tirst sleeve portion of each of said pair of caps to said casing, and adhesive strip means comprising a thermosetting resin aixed to both sides of each of'said pair of blade contacts and bonding said second sleeve portion of each of said pair of caps to one of said pair of blade contacts.

3. In an electric fuse the combination of a tubular casing of insulating material, a pair of terminal elements closing the ends of said casing, a pair of silver-plated blade contacts each projecting axially outwardly from one otsaid pair of terminal elements, fuse link means inside said casing` conductively interconnecting said pair of terminal elements, .a pair of caps of a substantially sulphur-free elastomer, each of said pair of caps comprising a first sleeve portion having an inner diameter substantially equal to the outer diameter of said casing mounted on one end of said casing, each of said pair of caps further comprising a second sleevel portion dening a duct having substantially the same cross-sectional coniguration as each of said pair of blade contacts, said second sleeve portion of each of said pair of caps being mounted lon one of said pair of blade contacts, means bonding said first sleeve portion of each of said pair of caps to said casing, and adhesive strip means comprising an epoxy resin, said strip means being aiiixed to Vboth sides of each of said pair of blade contacts and bonding said second sleeve portion of each of said pair of caps to one of said pair of blade contacts.

4. In an electric fuse the combination of a tubular casing of a synthetic-resin-glass-cloth laminate, a pair of metal plugs closing the ends of said casing, a pair of silver-plated blade contacts each projecting axially outwardly from one of said pair of metal plugs,'fuse link means inside said casing couductively interconnecting said pair of metal plugs, a pair of caps of substantially sulphur-free neoprene, each of said pair of caps comprising a first sleeve portion having an inner diameter substantially equal to the outer diameter of said casing mounted on one end of said casing, each of said pair of caps further comprising a second sleeve portion deiining a duct having substantially the same cross-sectional conguration as each of said pair of blade coutacts, said second sleeve portion of each of said pair of caps being mounted on one of said pair of blade con-4 tacts, means bonding said first sleeve portion of each said pair of caps to said casing, and strip means of a plastic material having an epoxy resin coating oneach side thereof, said strip means being alxed to both sides of each of said pair of blade contacts and bonding said second sleeve portion of each of said pair of caps to one of said pair of blade contacts.

5. In an electric fuse the combination of a tubular casing of insulating material, a pair of terminal elements closing the ends ot said casing, a pair of .contacts each projecting axially outwardly from one of said pair of terminal elements, fuse link means inside said casing conductively interconnecting said pair of terminal elements,

a pair of caps of an elastomer, each of said pair of caps comprising a rst sleeve portion mounted on said casing and a second sleeve portion mounted on one of said pair of contacts, and adhesive thermosetting strip means' bonding the inner surface of said second sleeve portion of each of said pair of caps to the surface of one of said pair of contacts. v

References Cited in the le of this patent' UNITED STATES PATENTS Genter Mar. 9, 1943 

